Direct conversion receiving apparatus and celluar phone

1. A direct conversion receiving apparatus, comprising: a gain control amplifier for input a base band signal and a gain switching control signal to control a gain, and variably amplify the base band signal based on the gain switching control signal; a high pass filter having an input terminal for input the output signal of said gain control amplifier, an output terminal, a first circuit including plural capacitors connected in parallel that are inserted in a path connecting the input terminal to the output terminal and switching effective total capacitance of the plural capacitors based on a first time constant switching control signal, and a second circuit including a resistor for providing a predetermined direct current voltage to the output terminal and switching the effective resistance value of the resistor based on a second time constant switching control signal; and a control circuit for output the gain switching control signal, and the first and second time constant switching control signals to control the cutoff frequency of said high pass filter according to the change of the gain control of said gain control amplifier, wherein, during the normal operation, said control circuit sets the capacitance values of the first circuit at a first capacitance value based on the first time constant switching control signal, and sets a resistance value of the second circuit at a first resistance value based on the second time constant switching control signal; and on switching the gain of said gain control amplifier, said control circuit switches the capacitance values of the first circuit to a second capacitance value that is smaller than the first capacitance value at a third timing after a second timing at which the gain of said gain control amplifier is switched, and returns the resistance value of the second circuit to the first resistance value at a fourth timing after the third timing.

2. The direct conversion receiving apparatus according to claim 1 , wherein said control circuit returns the capacitance values of the first circuit to the first capacitance value at a fifth timing after the fourth timing.

3. A direct conversion receiving apparatus, comprising: a gain control amplifier for input a base band signal and a gain switching control signal to control a gain, and variably amplify the base band signal based on the gain switching control signal; a high pass filter having an input terminal for input the output signal of said gain control amplifier, an output terminal, a first circuit including plural capacitors connected in parallel that are inserted in a path connecting the input terminal to the output terminal and switching effective total capacitance of the plural capacitors based on a first time constant switching control signal, and a second circuit including a resistor for providing a predetermined direct current voltage to the output terminal and switching the effective resistance value of the resistor based on a second time constant switching control signal; and a control circuit for output the gain switching control signal, and the first and second time constant switching control signals to control the cutoff frequency of said high pass filter according to the change of the gain control of said gain control amplifier, wherein the first circuit includes a first capacitor connecting the input terminal to the output terminal, and a serial circuit connected to the first capacitor in parallel and made of a second capacitor and a first time constant switching circuit connected to the second capacitor in series, said first time constant switching circuit being turned on/off on the basis of the first time constant switching control signal and connecting the second capacitor to the first capacitor in parallel when turned on; and the second circuit includes a first resistor providing a predetermined direct current voltage to the output terminal, and a second time constant switching circuit connected to the first resistor in parallel, said second time constant switching circuit being turned on/off on the basis of the second time constant switching control signal and causing a short-circuit in the first resistor when turned on.

4. The direct conversion receiving apparatus according to claim 3 , wherein a value of the first capacitance is not more than 1/100 of a value of the second capacitance.

5. The direct conversion receiving apparatus according to claim 3 , wherein during the normal operation, said control circuit turns off the second time constant switching circuit; and on switching the gain of the gain control amplifier, said control circuit turns on the second time constant switching circuit at a first timing prior to a second timing at which the gain of said gain control amplifier is switched.

6. The direct conversion receiving apparatus according to claim 3 , wherein during the normal operation, said control circuit turns on the first time constant switching circuit and turns off the second time constant switching circuit; and on switching the gain of the gain control amplifier, said control circuit turns off the first time constant switching circuit at a third timing after the second timing at which the gain of said gain control amplifier is switched, and turns off the second time constant switching circuit at a fourth timing after the third timing.

7. The direct conversion receiving apparatus according to claim 6 , wherein said control circuit turns on the first time constant switching circuit at a fifth timing after the fourth timing.

8. The direct conversion receiving apparatus according to any of claims 3 , wherein two or more stages connected in series are provided, and each stage includes said gain control amplifier and said high pass filter connected at the output side of said gain control amplifier.

9. The direct conversion receiving apparatus according to claim 8 , wherein the first circuit of said high pass filter in each stage is connected to said control circuit by a common control line; and the second circuit of said high pass filter in each stage is connected to said control circuit by a common control line.

10. A cellular phone, comprising: an antenna for receiving or transmitting a radio frequency signal; a transmitting apparatus that generates a signal which is to be transmitted through the antenna; and the direct conversion receiving apparatus according to claim 3 , that receives the radio frequency signal through the antenna to generate a base band signal.

11. A direct conversion receiving apparatus, comprising: a gain control amplifier for input a base band signal and a gain switching control signal to control a gain, and variably amplify the base band signal based on the gain switching control signal; a high pass filter having an input terminal for input the output signal of said gain control amplifier, an output terminal, a first circuit including plural capacitors connected in parallel that are inserted in a path connecting the input terminal to the output terminal and switching effective total capacitance of the plural capacitors based on a first time constant switching control signal, and a second circuit including a resistor for providing a predetermined direct current voltage to the output terminal and switching the effective resistance value of the resistor based on a second time constant switching control signal; and a control circuit for output the gain switching control signal, and the first and second time constant switching control signals to control the cutoff frequency of said high pass filter according to the change of the gain control of said gain control amplifier, wherein the first circuit includes a first capacitor connecting the input terminal to the output terminal, a serial circuit connected to the first capacitor in parallel and made of a second capacitor and a second resistance, and a first time constant switching circuit connected to the second resistor in parallel, said first time constant switching circuit being turned on/off on the basis of the first time constant switching control signal and causing a short circuit in the second resistor when turned on; and the second circuit includes a first resistor providing a predetermined direct current voltage to the output terminal and a second time constant switching circuit connected to the first resistor in parallel, said second time constant switching circuit being turned on/off on the basis of the second time constant switching control signal and causing a short circuit in the first resistor when turned on.

12. The direct conversion receiving apparatus according to claim 11 , wherein a value of the first capacitance is not more than 1/100 of a value of the second capacitance.

13. The direct conversion receiving apparatus according to claim 11 , wherein during the normal operation, said control circuit turns off the second time constant switching circuit; and on switching the gain of the gain control amplifier, said control circuit turns on the second time constant switching circuit at a first timing prior to a second timing at which the gain of said gain control amplifier is switched.

14. The direct conversion receiving apparatus according to claim 11 , wherein during the normal operation, said control circuit turns on the first time constant switching circuit and turns off the second time constant switching circuit; and on switching the gain of the gain control amplifier, said control circuit turns off the first time constant switching circuit at a third timing after the second timing at which the gain of said gain control amplifier is switched, and turns off the second time constant switching circuit at a fourth timing after the third timing.

15. The direct conversion receiving apparatus according to claim 14 , wherein said control circuit turns on the first time constant switching circuit at a fifth timing after the fourth timing.